Gases used in chip manufacture are highly toxic, and are required to be supplied to extremely high standards of purity. If particulates are deposited on the chip, expensive scrappage can result. There are numerous sources of particulates, some rather obvious such as leakage through a filter, and some not so obvious, such as particulates removed by the flowing gases from defective welds.
Discontinuities in the piping system can cause especial risk, because they can act as places for particulates to gather. Then when some physical event occurs which jars the system, perhaps no more than the slamming of a door, they can be released as a cloud and spoil large amounts of work-in-progress, much of which may have been well advanced.
As a consequence, very close tolerances must be observed when welding tubing lengths together, and in welding fittings to lengths of tubing. The abutting parts must be very accurately aligned, both axially and angularly, and when the weld is finished, it should neither project into the passage, nor recede from it.
Orbital welders are used for making these welds. A well-know welder to which this invention is especially adaptable is shown in U.S. Pat. No. 5,196,664 issued to Kevin McGushion on Mar. 23, 1993. Its disclosure is incorporated herein in its entirety for its showing of an orbital welder useful with this invention.
This invention is especially directed to the welding of a fitting to a tubing. Both the fitting and the tubing must accurately be held in place. Also, many fittings of the VCR type have extremely sensitive sealing faces. These metal faces are very smooth and clean, and are intended to be brought against a matching surface with the same properties to make a seal. It is essential that these surface not be touched, because any corrosion, roughness, or scratching would spoil a surface-to-surface abutment which is used to seal against leakage of very toxic gases.
Also, such fittings are intended to be completed by a nut which is captive on the completed welded assembly. It is necessary that the part of the fitting which is welded to a tubing not only be accurately aligned with that tubing, but that its bearing surface against which the nut is drawn must be properly aligned with the bearing surface on the nut.
It is an object of this invention to provide a workholder which will accomplish the above objectives in a device that is convenient to use.